Compound specific hydrogen isotope analysis of 1,2-dichloroethane: potential for delineating source and fate of chlorinated hydrocarbon contaminants in groundwater

A Delta Plus XL continuous flow gas chromatography/high-temperature conversion-isotope ratio mass spectrometer system (GC-TC-IRMS) with a liquid nitrogen trap installed at the end of the micropyrolysis oven was used to measure hydrogen isotope (delta H-2) values of 1,2-dichloroethane (1,2-DCA). The 1,2-DCA delta H-2 values were within uncertainty of the delta H-2 value for the same 1,2-DCA analyzed using off-line sample preparation and conventional dual inlet mass spectrometry, verifying that this system can accurately measure 1,2-DCA delta H-2 values. After 71 reproducible and accurate 1,2-DCA delta H-2 measurements had been obtained, the standard deviation on the mean of the cumulative 1,2-DCA delta H-2 measurements was greater than +/- 5 parts per thousand. The cumulative load of chlorine at this point was similar to 5.5 x 10(-6) moles, which may be the limit to the quantity of chlorine that can be input before the reproducibility of 1,2-DCA delta H-2 measurements is compromised. This study is the first to our knowledge to demonstrate a method for obtaining accurate and reproducible compound-specific delta H-2 values for chlorinated hydrocarbons at dissolved concentrations typical of field conditions. Paired delta H-2 and delta C-13 values suggest that dual parameter isotopic measurements can distinguish between different contaminant sources, as well as providing additional constraints on degradation pathways and contaminant remediation. Copyright (C) 2007 John Wiley & Sons, Ltd.